Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.32   7.365%   $200.0425   $200.04   $200.05   $200.00  
  Purchase #2 $14.94   11.568%   $16.6683   $16.67   $16.65   $16.70  
  Purchase #3 $232.98   12.454%   $261.9953   $262.00   $262.00   $262.00  
  Purchase #4 $191.45   13.719%   $217.715   $217.72   $217.70   $217.70  
  Purchase #5 $215.79   6.378%   $229.5531   $229.55   $229.55   $229.60  
  Purchase #6 $249.33   10.702%   $276.0133   $276.01   $276.00   $276.00  
  Purchase #7 $217.84   5.527%   $229.88   $229.88   $229.90   $229.90  
  7 purchase totals = $1,308.65       $1,431.8675   $1,431.87   $1,431.85   $1,431.90